1. Field of the Invention
The present invention relates to a projection exposure apparatus, an optical member built in the same, and a device manufacturing method.
2. Description of the Related Art
Along with an increase in the degree of integration of integrated circuits, it is demanded that a projection exposure apparatus for semiconductor manufacture should project by exposure a circuit pattern formed on a reticle onto the wafer surface with high resolving power. To attain high resolution, the projection exposure apparatus has a projection optical system which increases the NA and shortens the wavelength. A projection exposure apparatus which uses an ArF excimer laser (λ=193 nm) as a light source so that the NA exceeds 0.8 attains a resolving power of 0.1 μm. In recent years, there has been proposed an immersion exposure apparatus that aims at a finer exposure pattern by filling the space between the wafer and the final surface of the projection optical system with a liquid having a refractive index higher than 1. This proposal is expected to further improve the resolving power.
To manufacture a projection optical system with high resolving power, precision adjustment is necessary after its assembly. That is, the adjustment of the projection optical system includes an operation for improving the specification to have a satisfactory performance by adjusting the interval and decentering of lenses while repeating the optical evaluation of, for example, spherical aberration, coma aberration, and distortion aberration. The optical performance can be evaluated by observing a resist pattern obtained by building the projection optical system in the projection exposure apparatus, projecting a reticle pattern image onto a resist (photosensitive agent) applied to a wafer to form a latent image on it, and developing the latent image.
As described above, the conventional projection exposure apparatus requires checking the quality of the resist pattern to adjust the performance of the projection optical system. However, the resist pattern formation method requires a troublesome operation for causing the projection exposure apparatus to form a latent image pattern on a wafer coated with a resist and develop it, and causing a scanning electron microscope to observe the resist pattern.
It is known to build a Fizeau interferometer in the projection exposure apparatus to measure the wavefront aberration of the projection optical system built in the projection exposure apparatus (Japanese Patent Laid-Open Nos. 2002-013908 and 2005-333149 and Japanese Patent No. 3796369).
To accurately measure the wavefront aberration of the projection optical system, it is necessary to suppress environmental variations such as vibration in the interferometer system to several nm or less. The suppression of such environmental variations requires a length measurement system capable of position measurement on the order of several nm or less, and a driving unit capable of control on the order of several nm using the measurement result. However, mounting of such a high-accuracy, large-scale measurement control system in the projection exposure apparatus has a significant influence on the implementation and cost of the apparatus. To the contrary, it is difficult to suppress environmental variations such as vibration to several nm or less without using such a measurement control system. This makes it impossible to accurately measure wavefront aberration even by building a Fizeau interferometer in the exposure apparatus.